1Section 5 Potatoes

Updated May 2017Nutrient Management Guide (RB209)

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Using the Nutrient Management Guide (RB209)

Section 1 Principles of nutrient management and fertiliser use

Section 2 Organic materials

Section 3 Grass and forage crops

Section 4 Arable crops

Cereals

Oilseeds

Sugar beet

Peas and beans

Biomass crops

Section 5 Potatoes

Section 6 Vegetables and bulbs

Section 7 Fruit, vines and hops

Using the Nutrient Management Guide (RB209)This latest revision of RB209 is based on research carried out since the previous edition was published in 2010. The revision includes updated recommendations, including those for additional crops and information on the nutrient content of additional organic materials.

RB209 was first published in 1973 and was the first comprehensive set of fertiliser recommendations from the Ministry of Agriculture, Fisheries and Food (MAFF). RB209 stands for Reference Book 209.

To improve the accessibility of the recommendations and information AHDB’s Nutrient Management Guide (RB209) is published as seven sections that will be updated individually.

Further informationThe Nutrient Management Guide (RB209) will be updated regularly. Please email your contact details to AHDB so that we can send you new versions when they are published - comms@ahdb.org.uk

Always consider your local conditions and consult a FACTS Qualified Adviser if necessary.

RB209: Nutrient ManagementDownload the app for Apple or Android phones to access the current version of all sections of the guide. With quick and easy access to videos, information and recommendations from the guide, it is practical for use in the field.

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Using the Nutrient Management Guide (RB209) / Contents

Contents

Summary of the main changes from the previous edition 5Checklist for decision making 5Phosphate, potash and magnesium recommendations 6

Taking soil samples for phosphorus, potassium and magnesium 7Classification of soil analysis results into Indices 7Phosphate, potash and magnesium recommendations 8Timing of application 9

Sulphur recommendations 10Lime and micronutrient recommendations 11Calculating Soil Nitrogen Supply 11

Field Assessment Method 11Measurement Method 18

Nitrogen recommendations 21Identifying the variety determinancy group 21Identifying the growing season length 22Fine tuning nitrogen recommendations 22 Selecting the most appropriate fertiliser 23

Conversion tables 25Analysis of fertilisers and liming materials 26Glossary 27Acknowledgments 32

This section provides guidance for potato crops and should be read in conjunction with Sections 1 and 2. For each crop, recommendations for nitrogen (N), phosphate (P2O5) and potash (K2O) are given in kilograms per hectare (kg/ha). Magnesium (MgO) and sulphur (as SO3) are given in kg/ha where these nutrients are needed.

Recommendations are given for the rate and timing of nutrient application. The recommendations are based on the nutrient requirements of the crop being grown, while making allowance for the nutrients supplied by the soil.

When grown in soil with a good structure, potatoes are capable of producing extensive root systems that are efficient in taking up water and nutrients, therefore, every effort should be made to ensure seedbeds are free of compaction. The value of the potato crop is dictated by the marketable yield, not the total yield and, in consequence, decisions about fertiliser rates should be considered together with factors such as site selection and seed rates.

Because of the very wide range of varietal characteristics and quality requirements for different market outlets, guidance from a FACTS Qualified Adviser should be used when making decisions for specific crop

Further informationFertiliser Calculator potatoes.ahdb.org.uk/online-toolbox/fertiliser-calculator

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Summary of the main changes from the previous edition / Checklist for decision making

Summary of main changes from previous edition1. Overall presentation

a. Fertiliser recommendations for potatoes are now presented in Section 5: Potatoes that incorporates the relevant appendices.

2. New and revised recommendations

a. The guidance on assessing Soil Nitrogen Supply (SNS) has been revised to include guidance on when Soil Mineral Nitrogen (SMN) sampling can be most useful and interpretation of SMN analysis results.

b. The guidance on soil sampling for P, K and Mg analysis has been updated.

c. The number of varieties included in the determinacy grouping list has increased.

d. Against a background of decreasing sulphur emissions from UK industry, a recommendation to apply 25 kg SO3/ha where S deficiency may be likely has been included.

Further informationSoil management for potatoes potatoes.ahdb.org.uk/agronomy/soils

Think Soils www.ahdb.org.uk/thinksoils

AHDB Field drainage guide cereals.ahdb.org.uk/publications

Nitrate Vulnerable Zones www.gov.uk/guidance/nutrient-management-nitrate-vulnerable-zones

Information on irrigation and water management for potatoes potatoes.ahdb.org.uk/agronomy/water

Checklist for decision makingIndividual decisions for fertiliser use must be made separately for every field. Where more than one crop is grown in a field, these areas must be considered individually.

1. Confirm the crop to be grown and the intended market. Identify any crop quality criteria required by this market, eg dry matter content and skin finish.

2. Identify the dominant soil type in the cropped area (Section 1: Principles of nutrient management and fertiliser use).

3. Assess soil structure and take action to remove soil compaction, if necessary. Poor soil structure can restrict crop growth and results in poor nutrient and water use efficiency.

4. Carry out soil analysis for pH, P, K and Mg every 3–5 years (page 7). Target values to maintain in arable rotations are:

• Soil pH 6.5 (5.8 on peat soils)

• Soil P Index 2

• Soil K lower Index 2 (2-)

• Soil Mg Index 2

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Checklist for decision making / Phosphate, potash and magnesium recommendations

5. Identify the Soil Nitrogen Supply (SNS) Index of the field, either by using the Field Assessment Method (page 11) or the Measurement Method (page 18). The Measurement Method is recommended where nitrogen supply from crop residues is expected to be high (SNS of more than 120 kg N/ha for arable rotations), or are uncertain.

6. Calculate the total and crop-available nutrients from organic materials that have been applied since harvest of the previous crop, or which will be applied to the crop being grown (Section 2: Organic materials). Deduct these nutrients from the recommended rates given in the tables.

7. Also check if the field is within a Nitrate Vulnerable Zone (NVZ), consider the rules for application rates and timing for fertilisers and organic materials and adjust plans to comply with NVZ requirements.

8. Decide on the strategy for phosphate and potash use. This will be building up, maintaining or running down the soil Index (Section 1: Principles of nutrient management). Allow for any surplus or deficit of phosphate or potash applied to previous crops in the rotation.

9. Calculate the amount of phosphate and potash removed in the harvested crop according to targeted crop yield (page 8). This is the amount of these nutrients that must be replaced in order to maintain the soil at the current Index.

10. Using the tables, decide on the required rate of each nutrient. Decide on the optimum timings for fertiliser application, then find the best match for these applications using available fertilisers.

11. Check that the fertiliser spreader or sprayer is in good working order and has been recently calibrated (Section 1: Principles of nutrient management).

12. Keep an accurate record of the fertilisers and organic manures applied.

Phosphate, potash and magnesium recommendationsCurrent phosphate, potash and magnesium recommendations are based on achieving and maintaining target soil Indices for each nutrient in the soil throughout the crop rotation. Soil analysis is used as a basis for making fertiliser decisions and it should be done every 3–5 years.

Soil samples can be collected by walking in a ‘W’ pattern through a field following the steps on page 7. Identifying the major soil type and yield variation in the field is a key step in establishing the need for GPS sampling.

Most UK laboratories are members of the PAAG that offers farmers and advisers confidence in laboratory analysis.

• Proficiency tests (often called ring tests) carried out by Wageningen University, guaranteeing that analysis from any member can be trusted.www.wepal.nl

• List of UK laboratories www.nutrientmanagement.org/what-we-do/support-and-advice/

find-a-laboratory

• Sampling guidelines www.nutrientmanagement.org/library/sampling

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Phosphate, potash and magnesium recommendations

Taking soil samples for phosphorus, potassium and magnesium

Soil sampling must be done well to avoid misleading results and expensive mistakes.

• The soil in each field should be sampled every 3–5 years

• Collect samples at the same point in the rotation and well before growing a sensitive crop eg sugar beet

• Ideally, sample immediately after the harvest of the previous crop

• Do not sample within six months of a lime or fertiliser application (except nitrogen) and avoid sampling when the soil is very dry

• Do not take samples in headlands, or in the immediate vicinity of hedges, trees or other unusual features

• The soil sample must be representative of the area sampled. Areas of land known to differ in some important respects (eg soil type, previous cropping, applications of manure, fertiliser or lime) should be sampled separately. Small areas known to differ from the majority of a field should be excluded from the sample

• Ideally the sampled area should be no larger than four hectares

• Clean tools before starting and before sampling a new area

• Walk a ‘W’ pattern across the sampling area, stopping at least 25 times

• At each point collect a subsample (core) to 15 cm depth using a gouge corer or screw auger

• The subsamples should be bulked to form a representative sample and sent to the laboratory for analysis

• Use appropriate packaging (normally available from the laboratory) and label samples clearly, providing as much information about the field and crop as possible

On soils where acidity is known to occur, more frequent testing may be needed than the 4-year cycle used for phosphate, potash and magnesium. Since acidity can occur in patches, spot testing with a soil test kit across the field is often useful. Soil tests can also be useful on soils which contain fragments of free lime, since these can give a misleadingly high pH when analysed following grinding in the laboratory.

Classification of soil analysis results into Indices

The laboratory soil analysis results for P, K and Mg (in mg/kg dry soil) can be converted into soil Indices using Table 5.1.

Table 5.1 Classification of soil P, K and Mg analysis results into Indices

Index Phosphorus (P) Potassium (K) Magnesium (Mg)

Olsen P Ammonium nitrate extract

mg/litre

0 0–9 0–60 0–25

1 10–15 61–120 26–50

2 16–25 121–180 (2-) 181–240 (2+) 51–100

3 26–45 241–400 101–175

4 46–70 401–600 176–250

5 71–100 601–900 251–350

6 101–140 901–1,500 351–600

7 141–200 1,501–2,400 601–1,000

8 201–280 2,401–3,600 1,001–1,500

9 Over 280 Over 3,600 Over 1,500

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Phosphate, potash and magnesium recommendations

Phosphate, potash and magnesium recommendations

The phosphate recommendations are higher than that required to replace offtake and are intended to achieve optimum yield. The potash recommendations are required to replace the offtake and maintain target soil Indices. The larger recommended applications for soils at Index 0 and 1 will bring the soil to Index 2 over a number of years. By not applying fertiliser at Index 3 or above, soil will run down over a number of years to the target Index.

The amounts of phosphate and potash shown in Table 5.2 at Index 2 are those recommended to achieve a total yield of 50 t/ha. Crops grown on soil at Indices 0 and 1 would be expected to respond to the extra amounts of phosphate, potash and magnesium shown in Table 5.2.

There is no need to adjust the recommended phosphate rates if the target yield is higher or lower than 50 t/ha.

However, the potash recommendation at target or lower Indices can be adjusted when yield is likely to be larger or smaller than 50 t/ha by multiplying the difference in expected yield by 5.8 kg/t.

Table 5.2 Recommended phosphate, potash and magnesium rates for a crop yielding 50 t/ha of tubers

Points to consider • Recommendations assume good soil structure, water supply,

and pest and disease control

• Recommendations are given as phosphate (P2O5), potash (K2O) and magnesium oxide (MgO). Conversion tables (metric–imperial, oxide–element) are given on page 25

• Organic materials supply phosphate and potash which contribute to crop requirements. Don’t forget to make allowance for the phosphate and potash applied in organic materials (Section 2: Organic materials)

• All recommendations are given for the mid-point of each Index. The K recommendations for the lower half (2-) and upper half (2+) of K Index 2 are the same

• Where a soil analysis value (as given by the laboratory) is close to the range of an adjacent Index, the recommendation may be reduced or increased slightly, taking account of that given for the adjacent Index. Small adjustments of less than 10 kg/ha are generally not justified

• Where more or less phosphate and potash are applied than suggested in the tables, adjustments can be made later in the rotation

Example 5.1

At K Index 1, the potash recommendation for an expected yield of 70 t/ha is 330 + (20 x 5.8) = 446 kg K2O/ha. No adjustment for yield should be made where the soil Index is higher than target.

P, K or Mg Index

0 1 2 34 and higher

kg /ha

Phosphate (P2O5) 250 210 170 100 0

Potash (K2O) 360 330 300 150 0

Magnesium (MgO) 120 80 40 0 0

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Phosphate, potash and magnesium recommendations

The amount of phosphate recommended for soils at P Index 2 or 3 is more than sufficient to replace the phosphate removed by a 50 t/ha crop (about 50 kg P2O5). The surplus phosphate will help to maintain the soil at a target P Index 2 for an arable crop rotation and should be allowed for when assessing the need for phosphate for following crops.

On soils at P Index 0 and 1, the surplus phosphate will help increase the soil P Index and no allowance should be made when deciding the phosphate requirement of a subsequent crop. On soils at P Index 2 or below, a large proportion of the phosphate should be water-soluble.

The amount of potash recommended at K Index 2 will only replace the amount removed by a 50 t/ha crop and potash should be applied for the next crop in the rotation to maintain the soil at K Index 2. The extra amounts of potash shown for K Index 0 and 1 soils will slowly increase the soil K Index.

Figure 5.1 Potash deficiency Figure 5.2 Magnesium deficiency

Timing of application

All the phosphate should be applied in the spring and either worked into the seedbed or placed at planting.

Where more than 300 kg K2O/ha is required, apply half in late autumn/winter and half in spring. On light sandy soils, all the potash fertiliser should be applied after primary cultivation and no sooner than late winter. Large amounts of potash can sometimes reduce tuber dry matter content. If applicable, reference should be made to recommendations from the processing customer. Where this occurs, the decrease may be smaller when muriate of potash (MOP, potassium chloride) is replaced by sulphate of potash (SOP, potassium sulphate).

These recommendations should be used for both bed and ridge and furrow systems. Where fertiliser is placed, a small reduction in the recommended rate of phosphate could be considered.

Points to consider • Ensure the potash offtake is balanced by an application of potash

fertiliser on Index 2 soils

• Check the soil is maintained at Index 2 for both phosphate and potash by soil sampling every 3–5 years

© Eric Anderson, Scottish Agronomy © Eric Anderson, Scottish Agronomy

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Phosphate, potash and magnesium recommendations / Sulphur recommendations

Sulphur recommendationsPotato crops are not generally thought to be responsive to sulphur. However, atmospheric sulphur emissions have declined significantly and a yield response to sulphur is possible. If deficiency does occur, it is most likely to show first in crops grown on deep sand soils with low organic matter and in areas well away from industrial pollution.

Farmers are advised to monitor the sulphur requirements of their crops. Where sulphur deficiency has previously occurred or is expected, apply 25 kg SO3/ha as a sulphate-containing fertiliser in the seedbed.

Example 5.2

Soil analysis shows P Index 2 and K Index 2 and main crop potatoes are to be grown. The expected yield is 65 t/ha tubers.

Based on 1 t/ha of tubers containing 1 kg P2O5/ha and 5.8 kg K2O/ha, a crop yielding 65 t/ha will remove:

Phosphate 65 x 1.0 = 65 kg P2O5/ha

Potash 65 x 5.8 = 377 kg K2O/ha

However, Table 5.2 recommends 170 kg P2O5/ha and 300 kg K2O/ha for a crop yielding 50 t/ha.

For phosphate, the recommendation is much larger than the offtake because potatoes are likely to respond to extra phosphate at P Index 2. Therefore the phosphate application rate is not adjusted for non-standard yield in potatoes. The surplus phosphate, 105 kg P2O5/ha (170 - 65 = 105), should be allowed for when deciding on the phosphate application for the next crop(s) grown in the rotation.

For potash, the recommendation should be adjusted for the additional yield expected: 300 + (15 x 5.8) = 387 kg K2O/ha.

• Where organic manure is applied, it is important to calculate the quantity of nutrients added in the manure (Section 2: Organic Materials) and adjust the amount of fertiliser accordingly. Allowing for the nutrients in manure reduces the need for fertiliser, improves farm profits and reduces the risk of nutrient pollution of water

• Construct a nutrient balance sheet for each field and ensure the phosphate and potash offtake is balanced by an equivalent application of phosphate and potash on Index 2 soils. Check that the soil is maintained at Index 2 by soil analysis every 3–5 years

Figure 5.3 Sulphur deficiency

Points to consider • Organic materials can supply useful amounts of sulphur

(Section 2: Organic materials)

• Sulphur recommendations are given as SO3. Conversion tables (metric–imperial, oxide–element) are given on page 25. If applying liquid fertilisers, manufacturers can supply tables which convert kg/ha of nutrient to litres/ha of product

• Further information on the occurrence of sulphur deficiency and diagnostic methods can be found in Section 1: Principles of nutrient management and fertiliser use

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Lime and micronutrient recommendations / Calculating Soil Nitrogen Supply

Lime and micronutrient recommendationsAlthough essential for plant growth, in most cases the very small quantities of micronutrients needed for potatoes can be supplied from soil reserves. The only significant trace element deficiency in potatoes is manganese (Mn), which can occur on peaty, organic or sandy soils at high pH and on other soil types if over-limed.

Manganese deficiency usually occurs in patches during periods of rapid growth and can be treated by one or more foliar sprays of a suitable manganese-containing material.

Potatoes can tolerate a degree of soil acidity and are best grown at soil pH levels that are lower than for most other arable crops. However liming immediately before potatoes should be avoided unless the soil pH is very low, as this can increase the risk of common scab and manganese deficiency.

Calculating Soil Nitrogen Supply (SNS)Fields vary widely in the amount of nitrogen available to a crop before any fertiliser or manure is applied. This variation must be taken into account to avoid inadequate or excessive applications of nitrogen.

The Soil Nitrogen Supply (SNS) system assigns an Index of 0 to 6 to indicate the likely extent of this background nitrogen supply. The Index is used in the recommendation tables to select the amount of nitrogen, as manufactured fertiliser, manure or a combination of both that typically would need to be applied to ensure optimum yield.

The SNS Index for each field can be estimated either by the Field Assessment Method using records of soil type, previous cropping and winter rainfall, or by the Measurement Method. This uses measurements of Soil Mineral Nitrogen (SMN) plus estimates of nitrogen already in the crop (at the time of soil sampling) and of available nitrogen from the mineralisation of soil organic matter and crop debris during the period of active crop growth.

Field Assessment Method

The Field Assessment Method does not take account of the nitrogen that will become available to a crop from any organic manures applied since harvest of the previous crop. The available nitrogen from organic materials applied since harvest of the previous crop, or those that will be applied to the current crop, should be calculated separately using the information in Section 2: Organic Materials, and deducted from the fertiliser nitrogen application rates shown in the recommendation tables.

There are five essential steps to follow to identify the appropriate SNS Index:

Step 1. Identify the soil type for the field Step 2. Identify the previous crop Step 3. Select the rainfall range for the field Step 4. Identify the provisional SNS Index using the appropriate table Step 5. Make any necessary adjustments to the SNS Index

Figure 5.4 Manganese deficiency

©Blackthorn Arable

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Calculating Soil Nitrogen Supply

Step 1. Identify soil type for the fieldCareful identification of the soil type in each field is very important. The whole soil profile should be assessed to one metre depth for arable crops. Where the soil varies, and nitrogen is to be applied uniformly, select the soil type that occupies the largest part of the field.

The soil type can be identified using Figure 5.5, which categorises soils on their ability to supply and retain mineral nitrogen. The initial selection can then be checked using Table 5.3. Carefully assess the soil organic matter content when deciding if the soil is organic (10% to 20% organic matter for the purposes of this guide) or peaty (more than 20% organic matter). If necessary, seek professional advice on soil type assessments, remembering this will only need to be done once.

Is soil mainly peat?

Is soil dark and stains fingers black or grey?

Does moist soil feel rough and gritty?

Does moist soil feel silty (smooth and buttery)?

Can moist soil be rolled into a strong ball, or be moulded like plasticine?

Is subsoil (>40 cm depth) sand or sandstone based?

Is soil silty to 100 cm depth or more?

Is subsoil (>40 cm depth) clay based?

Is soil over chalk, limestone or other rock (excluding sandstone) which is within 40 cm of the soil surface?

Peaty soil

Organic soil

Light sand soil

Deep silty soil

Medium soils

Deep clayey soil

Shallow soil

YES

YES

YES

YES

YES

YES

YES

YES

YES

NO

NO

NO

NO

NO

NO

NO

NO

Figure 5.5 Soil category assessment

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Light sand soils Soils which are sand, loamy sand or sandy loam to 40 cm depth and are sand or loamy sand between 40– 80 cm, or over sandstone rock.

Soils in this category have poor water holding capacity and retain little nitrogen.

Soil category Description of soil types within category Properties

Medium soils

Organic soils

Shallow soils

Deep clayey soils

Mostly medium-textured mineral soils that do not fall into any other soil category. This includes sandy loams over clay, deep loams, and silty or clayey topsoils that have sandy or loamy subsoils.

Soils that are predominantly mineral but with between 10–20% organic matter to depth. These can be distinguished by darker colouring that stains the fingers black or grey.

Soils over impermeable subsoils and those where the parent rock (chalk, limestone or other rock) is within 40 cm of the soil surface. Sandy soils developed over sandstone rock should be regarded as light sand soils.

Soils with predominantly sandy clay loam, silty clay loam, clay loam, sandy clay, silty clay or clay topsoil overlying clay subsoil to more than 40 cm depth. Deep clayey soils normally need artificial field drainage.

Soils in this category have moderate ability to retain nitrogen and allow average rooting depth.

Soils in this category are able to retain more nitrogen than lighter soils and have higher nitrogen mineralisation potential.

Soils in this category are less able to retain or supply nitrogen at depth.

Deep silty soilsSoils of sandy silt loam, silt loam or silty clay loam textures to 100 cm depth or more. Silt soils formed on marine alluvium, warp soils (river alluvium) and brickearth soils are in this category. Silty clays of low fertility should be regarded as other mineral soils.

Soils in this category are able to retain more nitrogen than lighter soils and allow rooting to greater depth.

Soils in this category are able to retain more nitrogen than lighter soils.

Peat soils Soils that contain more than 20% organic matter derived from sedge or similar peat material. Soils in this category have very high nitrogen mineralisation potential.

Calculating Soil Nitrogen Supply

Table 5.3 Soil category assessment

Step 2. Identify previous cropUsually, this is straightforward but sometimes clarification may be needed:

High residual nitrogen vegetables (‘high N vegetables’) are leafy, nitrogen-rich Brassica crops such as calabrese, Brussels sprouts and some crops of cauliflower where significant amounts of crop debris are returned to the soil, especially in rotations where an earlier Brassica crop has been grown within the previous twelve months. To be available for crop uptake, this organic nitrogen must have had time to mineralise but the nitrate produced must not have been at risk to loss by leaching.

Medium residual nitrogen vegetables (‘medium N vegetables’) are crops such as lettuce, leeks and long-season Brassicas, such as Dutch white cabbage, where a moderate amount of crop debris is returned to the soil.

Low residual nitrogen vegetables (‘low N vegetables’) are crops such as carrots, onions, radish, swedes or turnips where the amount of crop residue is relatively small.

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Calculating Soil Nitrogen Supply

Step 3. Select low, moderate or high rainfallThe appropriate rainfall category should be identified, based on either annual rainfall or excess winter rainfall. Ideally, an estimate of excess winter rainfall is required because this is closely related to drainage by which nitrate will be lost through leaching. Figure 5.6 below shows long-term (1981–2010) average excess winter rainfall and in an average year can be used to select the rainfall category.

There are three SNS Index tables representing ‘low rainfall’ (annual rainfall less than 600 mm, or less than 150 mm excess winter rainfall), ‘moderate rainfall’ (between 600–700 mm annual rainfall, or 150–250 mm excess winter rainfall), and ‘high rainfall’ areas (more than 700 mm annual rainfall, more than 250 mm excess winter rainfall).

Step 4. Identify the provisional SNS Index using the appropriate tableTables 5.4 (low rainfall), 5.5 (moderate rainfall) and 5.6 (high rainfall) should be used where the field has not been in grass within the past three years. Select one of these tables according to rainfall for the field. Take account of the footnotes to the tables.

Higher than typical Indices can occur where there has been a history of grassland or frequent applications of organic manures. Soil analysis for Soil Mineral Nitrogen (SMN) is recommended in these situations.

If grass has been grown in the previous three years, also look at Table 5.7. Select the higher of the Index levels based on the last crop grown (from Table 5.4, 5.5 or 5.6) and that based on the grass history (Table 5.7).

Points to consider • Do not confuse SNS (Soil Nitrogen Supply) and SMN

(Soil Mineral Nitrogen)

• SMN is the measured amount of mineral nitrogen (nitrate-N plus ammonium-N) in the soil profile

• SNS = SMN (0–90 cm or maximum rooting depth in shallow soils over rock) + crop N (at time of sampling for SMN) + estimate of available N from mineralisation of organic matter

Figure 5.6 Excess winter rainfall (mm)

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Calculating Soil Nitrogen Supply

Table 5.4 Soil Nitrogen Supply (SNS) Indices for low rainfall (500–600 mm annual rainfall, up to 150 mm excess winter rainfall) – based on the last crop grown

Table 5.5 Soil Nitrogen Supply (SNS) Indices for moderate rainfall (600–700 mm annual rainfall, or 150–250 mm excess winter rainfall) – based on the last crop grown

Previous crop

Soil type

Lightsand soils or shallow soils over sandstone

Medium soils or shallow

soils not over

sandstone

Deep clayey soils

Deep silty soils

Organic soils

Peatsoils

Beans 1 2 3 3

All crops in SNS

Index 3, 4, 5 or 6.

Consult a FACTS Qualified Adviser.

All crops in SNS

Index 4, 5 or 6.

Consult a FACTS Qualified Adviser.

Cereals 0 1 2 2

Forage crops (cut) 0 1 2 2

Oilseed rape 1 2 3 3

Peas 1 2 3 3

Potatoes 1 2 3 3

Sugar beet 1 1 2 2

Uncropped land 1 2 3 3

Vegetables (low N)b 0 1 2 2

Vegetables (medium N)b 1 3 3a 3a

Vegetables (high N)b 2 4a 4a 4a

Previous crop

Soil type

Lightsand soils or shallow soils over sandstone

Medium soils or shallow

soils not over

sandstone

Deep clayey soils

Deep silty soils

Organic soils

Peatsoils

Beans 1 2 2 3

All crops in SNS

Index 3, 4, 5 or 6.

Consult a FACTS Qualified Adviser.

All crops in SNS

Index 4, 5 or 6.

Consult a FACTS Qualified Adviser.

Cereals 0 1 1 1

Forage crops (cut) 0 1 1 1

Oilseed rape 0 2 2 2

Peas 1 2 2 3

Potatoes 0 2 2 2

Sugar beet 0 1 1 1

Uncropped land 1 2 2 2

Vegetables (low N)a 0 1 1 1

Vegetables (medium N)a 0 2 3 3

Vegetables (high N)a 1 3 4 4

a. Index may need to be increased by up to 1 where significantly larger amounts of leafy residues are incorporated (see Step 5). Where there is uncertainty, soil sampling for SMN may be appropriate.

b. Refer to Step 2.

a. Refer to Step 2.

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Calculating Soil Nitrogen Supply

Table 5.6 Soil Nitrogen Supply (SNS) Indices for high rainfall (over 700 mm annual rainfall, or over 250 mm excess winter rainfall) – based on the last crop grown

Table 5.7 Soil Nitrogen Supply (SNS) Indices following ploughing out of grass leys

Previous crop

Soil type

Lightsand soils or shallow soils over sandstone

Medium soils or shallow

soils not over

sandstone

Deep clayey soils

Deep silty soils

Organic soils

Peatsoils

Beans 0 1 2 2

All crops in SNS

Index 3, 4, 5 or 6.

Consult a FACTS Qualified Adviser.

All crops in SNS

Index 4, 5 or 6.

Consult a FACTS Qualified Adviser.

Cereals 0 1 1 1

Forage crops (cut) 0 1 1 1

Oilseed rape 0 1 1 2

Peas 0 1 2 2

Potatoes 0 1 1 2

Sugar beet 0 1 1 1

Uncropped land 0 1 1 2

Vegetables (low N)b 0 1 1 1

Vegetables (medium N)b 0 1 1 2

Vegetables (high N)b 1a 2 2 3

a. Index may need to be lowered by 1 where residues incorporated in the autumn and not followed immediately by an autumn-sown crop.

b. Refer to Step 2.

SNS Index

Light sands or shallow soils over sandstone – all rainfall areas Year 1 Year 2 Year 3

All leys with 2 or more cuts annually receiving little or no manure1–2 year leys, low N1–2 year leys, 1 or more cuts3–5 year leys, low N, 1 or more cuts

0 0 0

1–2 year leys, high N, grazed3–5 year leys, low N, grazed3–5 year leys, high N, 1 cut then grazed

1 2 1

3–5 year leys, high N, grazed 3 2 1

Other medium soils and shallow soils – not over sandstone – all rainfall areas

All leys with 2 or more cuts annually receiving little or no manure1–2 year leys, low N1–2 year leys, 1 or more cuts3–5 year leys, low N, 1 or more cuts

1 1 1

1–2 year leys, high N, grazed3–5 year leys, low N, grazed3–5 year leys, high N, 1 cut then grazed

2 2 1

3–5 year leys, high N, grazed 3 3 2

Deep clayey soils and deep silty soils in low rainfall areas (500–600 mm annual rainfall)

All leys with 2 or more cuts annually receiving little or no manure1–2 year leys, low N1–2 year leys, 1 or more cuts3–5 year leys, low N, 1 or more cuts

2 2 2

1–2 year leys, high N, grazed3–5 year leys, low N, grazed3–5 year leys, high N, 1 cut then grazed

3 3 2

3–5 year leys, high N, grazed 5 4 3

Deep clayey soils and deep silty soils in moderate (600–700 mm annual rainfall) or high (over 700 mm annual rainfall) rainfall areas

All leys with 2 or more cuts annually receiving little or no manure1–2 year leys, low N1–2 year leys, 1 or more cuts3–5 year leys, low N, 1 or more cuts

1 1 1

1–2 year leys, high N, grazed3–5 year leys, low N, grazed3–5 year leys, high N, 1 cut then grazed

3 2 1

3–5 year leys, high N, grazed 4 3 2

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Calculating Soil Nitrogen Supply

The Indices shown in Table 5.7 assume that little or no organic manures has been applied. Where silage fields have received the organic manures produced by livestock that have eaten the silage and the manure has been applied in spring, they should be regarded as containing nitrogen residues equivalent to a previous grazing history.

‘Low N’ grassland means average annual inputs of less than 250 kg N/ha in fertiliser plus crop available nitrogen in manure used in the last two years, or swards with little clover.

‘High N’ grassland means average annual applications of more than 250 kg N/ha in fertiliser plus crop available nitrogen in manure used in the last two years, or clover-rich swards or lucerne.

Step 5. Make any necessary adjustment to the SNS Index for certain conditionsWhen using the Field Assessment Method, it is not necessary to estimate the amount of nitrogen taken up by the crop over winter. This is already taken into account in the tables.

Manure history: Where regular applications of organic manures have been made to previous crops in the rotation, increase the Index value by one or two levels depending on manure type, application rate and frequency of application.

Field vegetables as previous crop: On medium, deep silty or deep clayey soils, nitrogen residues in predominantly vegetable rotations can persist for several years especially in the drier parts of the country. This is likely to be especially evident following ‘high or medium N vegetables’. The SNS tables make some allowance for this long persistency of nitrogen residues but the Index level may need to be adjusted upwards particularly where:

• Winter rainfall is low

• The history of vegetable cropping is longer than one year

• Larger than average amounts of crop residue or unused fertiliser are left behind (see footnote to Table 5.4)

In rotations where vegetable crops are grown infrequently and where there is uncertainty, soil sampling for SMN may be appropriate.

Fertiliser residues from previous crop: The Index assessments assume that the previous crop grew normally and that it received the recommended rate of nitrogen applied as fertiliser and/or organic manures. The Index should be increased if there is reason to believe nitrogen residues are likely to be greater than normal and these residues will not be lost by leaching. This could occur where a cover crop was sown in autumn and grew well over winter. The Index may need to be adjusted downwards if there is reason to believe nitrogen residues are likely to be smaller than usual.

After any adjustment, the SNS Index can be used in the recommendation tables.Point to consider

• The nitrogen contribution from manures applied after harvest of the previous crop should not be considered when deciding the SNS Index; this contribution should be deducted from the recommended nitrogen application rate using the information in Section 2: Organic Materials

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Calculating Soil Nitrogen Supply

Measurement Method

This method is particularly appropriate where the SNS is likely to be large and uncertain. This includes:

• Fields with a history of organic manure application and vegetable rotations where the timing of residue incorporation can strongly affect Soil Mineral Nitrogen (SMN) for the following crop

• Fields where long leys or permanent pasture have been recently ploughed out (but not in the first year after ploughing out)

• Fields where there have been problems such as regular lodging of cereals, very high grain protein or nitrogen contents, or previous crop failure (for example, due to drought or disease)

• Fields where there is significant variation in soil texture and/or large amounts of crop residues are incorporated. Nitrogen residues also can be large following outdoor pigs

The SNS Index can be identified using the results of direct measurement of SMN to 90 cm depth in spring, 60 cm depth in autumn/early winter, or to maximum rooting depth in shallow soils over rock. An estimate of net mineralisable nitrogen must be added to the SMN result when calculating the SNS.

SNS is likely to be low on light sand and shallow soils that have not received regular additions of organic manure or crop residues, particularly in moderate to high rainfall areas. In this scenario, prediction of SNS using the Field Assessment Method is advised.

The Measurement Method is not recommended for peat soils, or in the first season after ploughing out long leys or permanent pasture, where net mineralisation can be very large and uncertain and the measured SMN may be a relatively small component of SNS. For these soils, the Field Assessment Method or local experience will be better guides to SNS.

The Measurement Method does not take account of the available nitrogen supplied from organic manures applied after the date of soil sampling for SMN. The available nitrogen from manures applied after sampling should be calculated separately using the information in Section 2: Organic Materials, and deducted from the nitrogen rate shown in the appropriate recommendation table.

The nitrogen contribution from manures applied before sampling for SMN will be largely taken account of in the measured value and should not be calculated separately.

When using the Measurement Method there are three steps to follow:

Step 1. Measure Soil Mineral Nitrogen (SMN) Step 2. Make an allowance for net mineralisable nitrogen Step 3. Identify Soil Nitrogen Supply (SNS) Index

Points to consider • Do not confuse Soil Nitrogen Supply (SNS) and Soil Mineral

Nitrogen (SMN)

• SMN is the measured amount of mineral nitrogen (nitrate-N plus ammonium-N) in the soil profile

• SNS = a measurement of SMN + an estimate of subsequent N mineralisation

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Calculating Soil Nitrogen Supply

In detail, these three steps are:

Step 1. Measure Soil Mineral Nitrogen (SMN)Soil sampling must be done well to avoid misleading results and expensive mistakes.

Guidance on how to collect a SMN sample

• In most situations, sampling in late winter or early spring before nitrogen fertiliser is applied gives slightly better predictions of SNS than sampling in the autumn because overwinter leaching is accounted for, especially in high rainfall areas or on shallow or light sand soils. On soils less prone to leaching, sampling in autumn or early spring is equally effective.

• Avoid sampling within two to three months of applying nitrogen fertiliser or organic manures, or within a month after sowing

• Areas of land known to differ in some important respects (eg soil type, previous cropping, application of manures or nitrogen fertiliser) should be sampled separately

• Do not sample unrepresentative areas, such as ex-manure heaps or headlands

• Avoid collecting and sending samples immediately before the weekend or a public holiday

• Samples must be taken to be representative of the area sampled. A minimum of 10–15 soil cores should be taken following a ‘W’ pattern across each field/area to be sampled

• In larger fields (10–20 ha), increase the number of cores to 15–20 unless the soil type is not uniform, in which case more than one sample should be taken. This can be done by dividing the field into smaller blocks from each of which 10–15 soil cores are taken

• Each position should be sampled at three depths in the spring: 0–30 cm, 30–60 cm and 60–90 cm. Sampling to 60 cm is adequate in the autumn

• Samples from each depth should be bulked to form a representative sample of that depth. If the bulk sample is too big, take a representative subsample to send to the laboratory; but do not stir the sample excessively

• Use appropriate packaging (normally available from the laboratory) and label samples clearly, providing as much information about the field and crop as possible

• Samples should be analysed within three days of sampling; samples must be kept cool (2–4˚C) but not frozen during storage or transport

It is important to avoid cross-contamination of samples from different depths. Using a mechanised 1 metre long gouge auger (2.5 cm diameter) is a satisfactory and efficient method but care must be taken to avoid excessive soil compaction and contamination between soil layers. If each depth layer is to be sampled individually by hand, a series of screw or gouge augers should be used where the auger diameter becomes progressively narrower as the sampling depth increases.

Analysis in the laboratorySamples should be analysed for nitrate-N and ammonium-N. Analytical results in mg N/kg should be converted to kg/ha, taking into account the dry bulk density of the soil, then summed to give a value for the whole soil profile. For the majority of mineral soils a ‘standard’ bulk density of 1.33 g/ml can be used and the calculation can be simplified to:

SMN (kg N/ha) = mg N/kg x 2 (for each 15 cm layer of soil)

SMN (kg N/ha) = mg N/kg x 4 (for each 30 cm layer of soil)

SMN (kg N/ha) = mg N/kg x 8 (for each 60 cm layer of soil)

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Calculating Soil Nitrogen Supply

Step 2. Make an adjustment for net mineralisable nitrogenNitrogen mineralised from soil organic matter and crop debris after soil sampling is a potentially important source of nitrogen for crop uptake. However, in mineral soils of low to average organic matter content (<4% in England and Wales or <10% in Scotland and Northern Ireland), the amount of net mineralisable nitrogen will be relatively small and for practical purposes, no further adjustment is needed when using the recommendations in this guide. The only exception being after cold winters, when an estimate of around 20 kg N/ha may be appropriate.

An adjustment may be needed where soil organic matter content is above average or where there has been a history of regular manure applications. In these situations, a commercial measurement of Additionally Available N (AAN) gives the most useful prediction of mineralisation.

As a guide, where measurement is not done, for every 1% organic matter above 4%, a topsoil may release an additional 10 kg N/ha. Therefore a soil that has a topsoil organic matter content of 10% may release around 60 kg/ha more potentially available nitrogen than an equivalent soil with 4% organic matter content.

However, some soils with an organic matter content of above 4% may release little nitrogen and local knowledge must be used when estimating mineralisable nitrogen. Therefore, it is not possible to specify a routine amount by which to adjust SNS based on soil organic matter level.

Add any adjustment for net mineralisable nitrogen to the total of SMN and nitrogen in the crop to give SNS.

Step 3. Identify the SNS Index

Table 5.8 Soil Nitrogen Supply (SNS) Index

Adopting changes to nitrogen useLarge SMN measurements can overestimate SNS and small SMN measurements can underestimate SNS. Uptake of soil N by crops is rarely less than 50 kg N/ha, so SNS estimates less than this should be treated as 50 kg N/ha and no less.

Unless high SNS results (>160 kg N/ha) are confidently expected, they should also be treated with caution. If SNS estimates indicate that large changes (either increases or decreases) in nitrogen fertiliser use are required, crops should be monitored closely through spring for signs of nitrogen deficiency or excess and the planned nitrogen strategy should be adjusted if necessary. It may be best for changes in nitrogen use to be introduced gradually over a few seasons so that the effect on crop performance can be monitored.

SNS SNS Index

Less than 60 0

61–80 1

81–100 2

101–120 3

SNS SNS Index

121–160 4

161–240 5

More than 240 6

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Nitrogen recommendations

Nitrogen recommendations

Identifying the variety determinacy group

Nitrogen recommendations split potato varieties into one of four groups according to their degree of determinacy (a measure of the crop’s capacity to maintain leaf production after the first appearance of flowers). AHDB research at NIAB-CUF has consistently shown that for a given length of growing season, indeterminate varieties (variety groups 3 and 4) require less nitrogen than determinate varieties (variety groups 1 and 2).

The variety groups shown in Table 5.9 include the ratings for those varieties included in previous editions of this guide and for other varieties based on NIAB trials and breeder/agent experience of foliage habit (determinacy is not the same as the NIAB foliage-maturity score).

In addition, factors such as total nutrient balance, water availability and seed management, will also influence foliage longevity. The list is provided as an indication of determinacy groups but you are advised to seek the latest information from your agronomist or seed supplier for any particular variety.

Group

1 2 3

Determinate varietiesPartially determinate

varietiesIndeterminate

varieties

Short haulm longevity Medium haulm longevity Long haulm longevity

Minerva Endeavour DaisyPremiere Harmony DesireeRocket Juliette Eos

Vales Emerald Kestrel FamboWinston Lady Claire Fianna

Lady Rosetta HermesMarfona Kerr's Pink

Maris Peer King EdwardMaritiema Lady Christl

Melody Lady ValoraMiranda Maris PiperMozart MoreneNadine NavanNicola Pentland Dell

Orchestra Pentland SquireOrla Picasso

Osprey RecordPentland Javelin Rooster

Rembrandt Russet BurbankRomano SanteSaxon Sassy

Shannon SaturnaShepody Slaney

Vivaldi Stemster Wilja Valor

Victoria

Table 5.9 Variety determinacy groups Information provided by NIAB-CUF and AHDB

Var

iety

Var

iety

Group

1 2 3 4

Determinate varieties

Partially determinate varieties

Indeterminatevarieties

Short haulm longevity

Medium haulm longevity

Long haulm longevity

Very long haulm longevity

Accord Atlantic Agria AsterixAnnabelle Amanda Ambo Cara

Anya Arcade Amora Lady BalfourColmo Carlingford Cabaret MarkiesEstima Charlotte Caesar Royal

Innovator Courage Cosmos Vales EverestMaris Bard Dundrod Cultra Vales Sovereign

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Nitrogen recommendations

Identifying growing season length

The length of the growing season is the number of days between 50% emergence and haulm death from either natural senescence or defoliation. Table 5.10 Recommended N application rate for potatoes (kg/ha) per season length and variety determinacy group

Length ofgrowing season

Variety determinacy

group

SNS Index

0 and 1 2,3 and 4 5 and 6

kg N/ha

<60 days

1 100–140 70–110 40–60

2 80–120 50–80 0–40

3 60–100 40–70 0–40

4a N/A N/A N/A

60–90 days

1 160–210 130–160 90–120

2 100–160 60–120 40–80

3 60–140 40–100 0–60

4 40–80 20–40 0–40

90–120 days

1 220–270 190–220 150–180

2 150–220 110–160 80–120

3 110–180 80–100 40–60

4 80–140 40–60 0–40

>120 days

1 N/A N/A N/A

2 190–250 150–180 120–150

3 150–210 120–140 80–100

4 100–180 60–80 20–40

One of the following four options should be selected in Table 5.10:

• Less than 60 days

• Between 60 and 90 days

• Between 90 and 120 days

• More than 120 days

Nitrogen increases yield by prolonging haulm life. It has no consistent effect on tuber numbers and, consequently, where it gives an increase in yield, the mean tuber size will be greater.

Similarly, if the intended season length is at the lower (or upper) end of the ranges given in Table 5.10, consider nitrogen applications at the lower (or upper) ends of the ranges given.

Fine tuning nitrogen recommendations

Planting dateThe recommendations assume that loss of ground cover should begin close to the time of defoliation and harvest. If crops are planted later than intended but the defoliation date remains unaltered, this will reduce the length of the growing season, which will justify a reduction in the nitrogen application rate.

Cold soilsCrops planted into cold soils are slow to emerge and often have restricted canopy development. For determinate crops planted into cold soils and where emergence is delayed but the intended season length remains the same, consider increasing the amount of nitrogen applied by 15–20 kg N/ha.

Also, for all varieties at the upper end of season length, consider using the nitrogen recommendation from the upper end of the range.

N/A= Not Applicable

a. Consideration can be given to group 4 varieties grown for less than 60 days with the addition of 0 to 40 kg/ha for all soil Indices.

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Nitrogen recommendations

Timing of nitrogen applicationIf top dressing is planned for management reasons or to reduce the risk of leaching for crops grown on light sand and shallow soils, apply about two-thirds of the nitrogen recommendation in the seedbed and the remainder shortly after emergence. Aim to apply all the nitrogen by the time of tuber initiation (about three weeks after 50% plant emergence).

For other crops, apply all of the recommended nitrogen in the seedbed.

The effect of irrigationDifferences in the nitrogen requirement of irrigated or rain-fed crops are generally small, however, nitrogen rates could be reduced by 15–20 kg N/ha in rain-fed, determinate crops in order to achieve the same yield.

Placement of nitrogen in bed systemsThe same recommendations should be used for bed as well as ridge and furrow systems. Where fertiliser application methods reduce the amount of nitrogen falling into furrow-bottoms (eg placement or banded applications) reductions in the total amount of nitrogen applied could be considered.

Problems with previous potato cropsIf similar crops grown in previous seasons have had problems with excessive canopy production and were defoliated at complete ground cover, consider reducing the nitrogen application rate.

Similarly, if there have been frequent problems with delayed skin-set, consider reducing the nitrogen rate towards the lower end of the recommended range.

Allowances should be made for the likely supply of nitrogen from incorporated cover crop residues. However, growers will need guidance on how to assess the amount of N taken up by the cover crop and what proportion is likely to be made available. Growers should refer to Section 1: Principles of nutrient management and fertiliser use, for further information.

Further informationIrrigation and water use best practice guide for potatoes potatoes.ahdb.org.uk/agronomy/water

Selecting the most appropriate fertiliser

For a single nutrient, the recommended amount can be applied using a straight fertiliser. Where more than one nutrient is required, a compound or blended fertiliser can be used. In this case, the compound or blend selected will depend on the ratio of the nutrients in the fertiliser; the amount applied should give as near the recommended amount of each nutrient as possible.

Often it will not be possible to match exactly the recommendations with available fertilisers. In most cases, the first priority is to get the amount of nitrogen correct because crops respond most to nitrogen. Slight variation in the rates of phosphate or potash will have less effect on yield, especially on Index 2 soils, and any discrepancy can be corrected in fertiliser applications to future crops. The approximate nutrient content of commonly used fertilisers is described on page 26.

Points to consider Excess (or ‘insurance’) applications of nitrogen can:

• Decrease yield especially in shorter season indeterminate varieties

• Increase haulm size, prevent effective penetration of fungicidal sprays, delay natural senescence and create difficulties with desiccation

• Delay achievement of skin set

• Sometimes affect achievement of target dry matter concentrations.

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Example 5.3Field location: Cambridge

Variety: Maris Piper

Intended planting date: 15 April

Intended defoliation date: 15 September

Soil type: Medium

Previous crop: Winter barley

Use of organic manure: No

Other information: All N to be applied before tuber initiation; no previous problems with either premature canopy senescence or excess canopy production.

1. Calculate SNS. It is a low rainfall area, the soil type is medium and the previous crop is a cereal. Table 5.4 indicates that the SNS Index = 1. 2. Identify variety group using Table 5.9, Maris Piper is variety group 3. 3. Calculate length of growing season. The crop is to be planted mid-April (emerging mid-May) and defoliated in mid-September. Total 125 days (>120 days). 4. Use Table 5.10 to calculate N requirement. 180 kg N/ha (150–210 kg N/ha). 5. Assess factors to fine-tune recommendation (pages 22–23). The crop should have an effective root system and applied N should be efficiently used, but the growing season is long, 180 kg N/ha. 6. Include allowance for applied organic manures. No manures applied, 0 kg N/ha. 7. Manufactured-N fertiliser 180 kg N/ha.

Example 5.4Field location: Somerset

Variety: Estima

Intended planting date: 30 April

Intended defoliation date: 15 August

Soil type: Medium

Previous crop: Oilseed rape

Use of organic manure: Yes

Other information: All N to be applied before tuber initiation 40t/ha cattle FYM applied in winter after four months storage, and ploughed in one week later.

1. Calculate SNS. It is a high rainfall area and the soil type is medium. Table 5.6 indicates that the SNS Index = 1. 2. Identify variety group using Table 5.9. Estima is variety group 1. 3. Calculate length of growing season. Planted end April (emerging end May) and defoliated in mid August = 80 days. Season length = 60 to 90 days. 4. Use Table 5.10, to calculate N Requirement 185 kg N/ha (160–210 kg N/ha). 5. Assess factors to fine-tune recommendations (pages 22–23). It was an unusually cold spring, crop slow to emerge with the potential for a restricted canopy therefore consider additional N, 200 kg N/ha. 6. Allowance for applied organic manures 40 t/ha of cattle FYM, 24 kg/ha of crop-available N. 7. Manufactured-N fertiliser 176 kg N/ha.

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Conversion tables

Conversion tablesMetric to imperial1 tonne/ha 0.4 tons/acre 100 kg/ha 80 units/acre 1 kg/tonne 2 units/ton 10 cm 4 inches 1 m3 220 gallons 1 m3/ha 90 gallons/acre 1 kg/m3 9 units/1000 gallons 1 kg 2 unitsNote: a ‘unit’ is 1% of 1 hundredweight, or 1.12lbs.

Imperial to metric1 ton/acre 2.5 tonnes/ha100 units/acre 125 kg/ha1 unit/ton 0.5 kg/tonne1 inch 2.5 cm1,000 gallons 4.5 m3

1,000 gallons/acre 11 m3/ha1 unit/1,000 gallons1 unit 0.5 kg

Element to oxideP to P2O5 Multiply by 2.291K to K2O Multiply by 1.205Mg to MgO Multiply by 1.658S to SO3 Multiply by 2.5Na to Na2O Multiply by 1.348Na to salt Multiply by 2.542

Oxide to elementP2O5 to P Multiply by 0.436K2O to K Multiply by 0.830MgO to Mg Multiply by 0.603SO3 to S Multiply by 0.4Na2O to Na Multiply by 0.742Salt to Na Multiply by 0.393

Fluid fertiliser kg/tonne (w/w basis) to kg/m3 Multiply by specific gravity (w/v basis)

Further informationConversion calculators cereals.ahdb.org.uk/tools/agronomy-calculators

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Analysis of fertilisers and liming materials

Analysis of fertilisers and liming materialsThe materials listed below are used individually and some are used as components of compound or multi-nutrient fertilisers. The chemical and physical forms of nutrient sources, as well as growing conditions, can influence the effectiveness of fertilisers. A FACTS Qualified Adviser can give advice on appropriate forms for different soil and crop conditions.

The reactivity, or fineness of grinding, of liming materials determines their speed of action. However, the amount of lime needed is determined mainly by its neutralising value.

Nitrogen fertilisers Typical % nutrient contentAmmonium nitrate 33.5–34.5% NLiquid nitrogen solutions 18–30% N (w/w)Calcium ammonium nitrate (CAN) 26–28% NAmmonium sulphate 21% N, 60% SO3Urea 46% NCalcium nitrate 15.5% N, 26% CaO

Phosphate fertilisersSingle superphosphate (SSP) 18–21% P2O5, typically 30% SO3Triple superphosphate (TSP) 45–46% P2O5Di-ammonium phosphate (DAP) 18% N, 46% P2O5Mono-ammonium phosphate (MAP) 12% N, 52% P2O5Rock phosphate (eg Gafsa) 27–33% P2O5

Potash, magnesium and sodium fertilisersMuriate of potash (MOP) 60% K2OSulphate of potash (SOP) 50% K2O, 45% SO3Potassium nitrate 13% N, 45% K2OKainit 11% K2O, 5% MgO, 26% Na2O, 10% SO3Sylvinite Minimum 16% K2O, typically 32% Na2OKieserite (magnesium sulphate) 25% MgO, 50% SO3Calcined magnesite Typically 80% MgOEpsom salts (magnesium sulphate) 16% MgO, 33% SO3Agricultural salt 50% Na2O

Sulphur fertilisersAmmonium sulphate 21% N, 60% SO3Epsom salts (magnesium sulphate) 16% MgO, 33% SO3Elemental sulphur Typically 200–225% SO3 (80–90% S)Quarried gypsum (calcium sulphate) 40% SO3Polyhalite (e.g. Polysulphate) Minimum 48% SO3, 14% K2O, 6% MgO, 17% CaO.

Liming materials Neutralising Value (NV)Ground chalk or limestone 50–55Magnesian limestone 50–55, over 15% MgOHydrated lime c.70Burnt lime c.80Sugar beet lime 22–32 + typically 7–10 kg P2O5, 5–7 kg MgO, 3–5 kg SO3/tonne

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Glossary

Glossary

Available (nutrient) Form of a nutrient that can be taken up by a crop immediately or within a short period so acting as an effective source of that nutrient for the crop.

Clay Finely divided inorganic crystalline particles in soils, less than 0.002 mm in diameter.

Content (nutrient) Commonly used instead of the more accurate ‘concentration’ to describe nutrients in fertiliser or organic manure. For example, 6kg N/t often is described as the nitrogen content of a manure.

Cover crop A crop sown primarily for the purpose of taking up nitrogen from the soil and which is not harvested. Also called green manure.

Crop available The total nitrogen content of organic manure that isnitrogen available for crop uptake in the growing season in which

it is spread on land.

Crop nitrogen The amount of crop available nitrogen that must berequirement applied to achieve the economically optimum yield.

Deposition Transfer of nutrients from the atmosphere to soil or to plant surfaces. The nutrients, mainly nitrogen and sulphur, may be dissolved in rainwater (wet deposition) or transferred in particulate or gaseous forms (dry deposition).

Excess winter Rainfall between the time when the soil profile becomesrainfall fully wetted in the autumn (field capacity) and the end of

drainage in the spring, less evapo-transpiration during this period (ie, water lost through the growing crop).

FACTS UK national certification scheme for advisers on crop nutrition and nutrient management. Membership renewable annually. A FACTS Qualified Adviser has a certificate and an identity card.

Fertiliser See Manufactured fertiliser.

Fluid fertiliser Pumpable fertiliser in which nutrients are dissolved in water (solutions) or held partly as very finely divided particles in suspension (suspensions).

Grassland Land on which the vegetation consists predominantly of grass species.

Green manure See Cover crop.

Incorporation A technique (discing, rotovating, ploughing or other methods of cultivation) that achieves some mixing between an organic manure and the soil. Helps to minimise loss of nitrogen to the air through volatilisation, and nutrient runoff to surface waters.

Leaching Process by which soluble materials such as nitrate or sulphate are removed from the soil by drainage water passing through it.

Ley Temporary grass, usually ploughed up one to five years (sometimes longer) after sowing.

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Glossary

Liquid fertiliser See Fluid fertiliser.

Manufactured Any fertiliser that is manufactured by an industrialfertiliser process. Includes conventional straight and NPK

products (solid or fluid), organo-mineral fertilisers, rock phosphates, slags, ashed poultry manure and liming materials that contain nutrients.

Micronutrient Boron, copper, iron, manganese, molybdenum and zinc that are needed in very small amounts by crops. Cobalt and selenium are taken up in small amounts by crops and are needed in human and livestock diets.

Mineral nitrogen Nitrogen in ammonium (NH4) and nitrate forms (NO3).

Mineralisable Organic nitrogen that is readily converted to ammoniumnitrogen and nitrate by microbes in the soil, for example, during

spring.

Mineralisation Microbial breakdown of organic matter in the soil, releasing nutrients in crop-available, inorganic forms.

Neutralising Percentage calcium oxide (CaO) equivalent in a material.value (NV) 100 kg of a material with a neutralising value of 52% will

have the same neutralising value as 52 kg of pure CaO. NV is determined by a laboratory test.

Nitrate vulnerable Areas designated by Defra as being at risk fromzones (NVZs) agricultural nitrate pollution.

Offtake Amount of a nutrient contained in the harvested crop (including straw, tops or haulm) and removed from the field. Usually applied to phosphate and potash.

Olsen P Concentration of available P in soil determined by a standard method (developed by Olsen) involving extraction with sodium bicarbonate solution at pH 8.5. It is the main method used in England, Wales and Northern Ireland and the basis for the Soil Index for P.

Organic material Any bulky organic nitrogen source of livestock, human or plant origin, including livestock manures, biosolids (sewage sludge), compost, digestate and waste-derived materials.

Organic soil Soil containing between 10% and 20% organic matter (in this manual). Elsewhere, sometimes refers to soils with between 6% and 20% organic matter.

Peaty soil (peat) Soil containing more than 20% organic matter.

Placement Application of fertiliser to a zone of the soil usually close to the seed or tuber.

Sand Soil mineral particles larger than 0.05 mm.

Silt Soil mineral particles in the 0.002–0.05 mm diameter range.

SNS Index Soil Nitrogen Supply expressed in seven bands or Indices, each associated with a range in kg N/ha.

Soil Index Concentration of available P, K or Mg, as determined(P, K or Mg) by standard analytical methods, expressed in bands or

Indices.

Soil Mineral Ammonium and nitrate nitrogen measured by theNitrogen (SMN) standard analytical method and expressed in kg N/ha.

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Glossary

Soil Nitrogen The amount of nitrogen, (kg N/ha) in the soil thatSupply (SNS) becomes available for uptake by the crop in the growing

season, taking account of nitrogen losses.

Soil organic matter Often referred to as humus. Composed of organic compounds ranging from undecomposed plant and animal tissues to fairly stable brown or black material with no trace of the anatomical structure of the material from which it was derived.

Soil texture Description based on the proportions of sand, silt and clay in the soil.

Soil type Description based on soil texture, depth, chalk content and organic matter content.

Target soil Index Lowest soil P or K Index at which there is a high probability crop yield will not be limited by phosphorus or potassium supply. See Soil Index (P, K or Mg).

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Notes

31

Notes

AcknowledgementsFunding for the production of this section of the Nutrient Management Guide (RB209) is provided by AHDB.

Revision of the Fertiliser Manual (RB209) to create the Nutrient Management Guide (RB209) has been overseen by the UK Partnership for Crop Nutrient Management which is led by AHDB.

AHDB wishes to thank all those who freely give their time to serve on the Steering Group as well as the Arable, Horticulture and Livestock Technical Working Groups. AHDB also wishes to thank the numerous farmers and growers across the country who host trials.

Arable Technical Working Group: Agrii, AHDB, BBRO, Bunn Fertiliser Ltd, C F Fertilisers UK Ltd, Catchment Sensitive Farming, Cropwell, DAERA, Defra, Frontier Agriculture Ltd, H. L. GWE Biogas Ltd, Hutchinson Ltd, K+S UK & Eire Ltd, OMEX Agriculture Ltd, Paul Towns Ltd, Pepsico International, PGRO, Potash Development Association, Scottish Government, Velcourt Ltd, Welsh Government and Yara UK Ltd.

Steering Group: AHDB, Agricultural Industries Confederation, Association of Independent Crop Consultants, BBRO, Catchment Sensitive Farming, DAERA, Defra, FACTS, PGRO, Professional Nutrient Management Group, Scottish Government and Welsh Government.

Funding for trials was provided by:

Research providers: This revision of this section of the Nutrient Management Guide (RB209) was carried out by a consortium led by ADAS.

The Nutrient Management Guide (RB209) contains public sector information licensed under the Open Government Licence (OGL) v3.0 www.nationalarchives.gov.uk/doc/open-government-licence/version/3

Cambridge University Potato Growers Research Association

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